Many medical imaging applications require knowledge of patient respiratory activity. Applications such as radiation therapy planning and pediatric imaging without breath hold can benefit from extraction of respiratory motion during the image acquisition process.
Current methodology utilizes an external sensor to obtain this respiratory activity or respiratory waveform since the breathing cycle exhibits different phases. An example of such a system uses the Varian Real-Time Position Management (RPM) Respiratory Gating System. See, Mageras G. et al., Initial clinical evaluation of a respiratory gating radiotherapy system, Engineering in Medicine and Biology Society, 2000, Proceedings of the 22nd Annual International Conference of the IEEE (2000), Volume 3, Pages 2124-2127. The RPM tool places a small reflective marker on the chest wall of the patient, and a video monitor tracks its position. Video analysis and signal processing steps produce the respiratory waveform based on the movement of the sensor throughout the respiratory cycle. In addition to complicating the patient setup and radiotherapy planning workflow, these respiratory monitoring devices can be expensive.
In four dimensional Computed Tomography (4DCT) respiratory gating utilizes a small reflective marker placed on the patient's chest or abdomen that can be detected by an infrared camera placed at the foot of the patient table. Respiratory gating allows therapists to track the patient's respiratory cycle both at the time of the CT scan for imaging and at the time of treatment. As the patient breathes, the marker is vertically displaced according to the patient's respiratory cycle and the infrared camera records the position of the marker. This information is then used to determine the patient respiratory phase at the time of Computed Tomography (CT) image acquisition. CT images are generated at multiple locations along the patient's chest and abdomen. The CT images are then retrospectively sorted into phases according to the information recorded by the infrared camera. The result of reconciling the images to the infrared camera respiratory waveform is a four dimensional (4D) image set. This 4D image set consists of a 3D volumetric image data set generated for each of multiple respiratory phases, image set of the lungs and surrounding area throughout the respiratory cycle. This is particularly useful for radiation therapy, as it is clinically relevant to understand the motion of lung and abdominal tumors throughout the respiratory cycle in order to properly plan radiation treatment. As radiation therapy technology emerges, high quality 4D reconstructions and easily implemented respiratory gating capability become increasingly important for precise tumor tracking and minimization of patient preparation and planning time.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for extracting motion from projection data that is directly related to actual respiratory activity.